In one form of multiribbed power transmission belt, a problem has arisen in that cracks tend to form in the ribs extending inwardly from the tip to the root of the ribs, such as when the belt is reversely bent in the drive system.
It is conventional in such prior art belts to provide distributed short fibers oriented transversely to th longitudinal extent of the belt and distributed in the rib portion.
One attempted solution to this problem has been the provision of a rib construction wherein the inner portion of the rib is formed to have a lower hardness than the outer portion thereof adjacent the cushion rubber layer carrying the tensile cords of the belt.
While the provision of the softer inner rubber tends to prevent the undesirable crack formation, the soft rubber tends to wear rapidly in engagement with the confronting surfaces of the pulley grooves. Further, the engagement of the inner portion of the ribs with the surfaces of the pulley grooves introduces stresses in the ribs, tending to develop cracks therein.